The invention relates to a picture display device comprising at least one compartment containing an ionizable gas, in which walls of the compartment are provided with electrodes for selectively generating a plasma discharge of the ionizable gas during operation, and an electro-optical layer of a material having an optical property which is dependent on the discharge state of the plasma discharge.
Picture display devices for displaying monochromatic or color images comprise, inter alia, plasma-addressed liquid crystal display devices, referred to as PALC displays, and (DC) plasma display panels (PDPs). The PALC displays and PDPs are used as television and computer displays and are preferably of the flat-panel type.
A picture display device of the type described in the opening paragraph is known from PCT patent application WO-A-99/04408 (PHN 16458). The flat-panel picture display device described in this document comprises a display screen having a pattern of (identical) data storage or display elements and a multitude of compartments. The compartments are filled with an ionizable gas and provided with electrodes for (selectively) ionizing the ionizable gas during operation. In the known picture display device, the compartments have the shape of parallel, elongate channels (formed in a channel plate) which function as selection means for the picture display device (the plasma-addressed row electrodes). By applying a DC voltage difference across the electrodes in one of the channels of the channel plate, electrons are emitted (from the cathode) which ionize the ionizable gas, thereby forming a plasma (plasma discharge). When the voltage across the electrodes in one channel is switched off and the gas is de-ionized, a subsequent channel is switched on. On the display screen side of the picture display device, the compartments are closed by a (thin) dielectric layer (xe2x80x9cmicrosheetxe2x80x9d). The picture display device further comprises a layer of an electro-optical material provided between the channel plate and a substrate provided with further electrodes which function as the data electrodes or column electrodes of the picture display device. The picture display device is formed by the assembly of the channel plate with the electrodes and the ionizable gas, the dielectric layer, the layer of the electro-optical material and the substrate with the further electrodes.
In the known picture display device, the light transmissibility of the electro-optical layer is determined, during operation, by the plasma, discharge (also dependent on the voltage at the column electrodes).
In a plasma display panel, a plasma discharge is used to directly excite a layer comprising electroluminescent phosphors of display elements, in which (electrons of) the ionized gas in the compartment itself excite(s) the phosphors. In an alternative embodiment of a plasma display panel, a plasma discharge is used to generate light (for example, UV light) in which the light excites a layer comprising photoluminescent phosphors of display elements.
In the known display device, the energy consumption of such picture display devices is reduced by providing at least one of the electrodes with a layer comprising particles of a sputter-resistant material.
Since a (DC) plasma discharge is used in the picture display device, the electrodes in the compartment are subject to an ion bombardment and, generally, the electrodes are made of a sputter-resistant material, or the electrodes are preferably provided with a sputter-resistant layer. The use of sputter-resistant material increases the resistance of the electrodes against sputtering. In said patent application, at least one of the electrodes is provided with such a layer comprising (macroscopic) particles of a sputter-resistant material or xe2x80x9crefractory materialxe2x80x9d.
Practice has proved that such a layer comprising a sputter-resistant material generally adheres poorly to the electrodes. It is an object of the present invention to obviate this drawback.
To this end, a picture display device according to the invention is characterized in that at least one of the electrodes is provided with a layer comprising sputter-resistant material and a frit, in which the frit and the sputter-resistant material have a mass ratio Mfrit/Msrm of at least 0.9, in which Mfrit and Msrm represent the mass of frit and the mass of sputter-resistant material, respectively, per surface unit.
The mass ratio Mfrit/Msrm is preferably at least 1 or more. It has been found that very satisfactorily adhesive layers can be obtained with these ratios. At a mass ratio from about 3.5, however, the generated plasma is unstable.
Sputter-resistant material suitable for the purpose of the invention comprises rare earth borides, for example LaB6 or GdB6, or ruthenium oxide (RuO2).
The sputter-resistant material can be prepared with the frit which is, for example, a glass frit in the suitable mixing ratio and subsequently provided on the electrodes.
In an alternative embodiment according to the invention, the layer of sputter-resistant material is provided on a (glass) frit on (at least one of) the electrodes. By manufacturing the layer in two steps, parts of the sputter-resistant material fill pores of the (glass) frit layer. In this respect it is to be noted that WO-A-99/04408 (PHN 16458) already states the possibility of improving the adhesion of the layer by adding very finely ground glass frit (typical grain sizexe2x89xa61 xcexcm) to the particles of the sputter-resistant material. In contrast to the present invention, a small quantity of frit is chosen in the method described in this document, because the presence of frit particles generally does not lead to a reduction of the effective surface of the sputter-resistant material, which is undesirable for a maximal secondary emission coefficient of the layer of sputter-resistant material.